The man and the lift

Back in 1998, I interviewed for a product manager position with the HR director of the Peroni brewery, a brilliant person who, after the usual stages of the interview, asked me to solve the following puzzle:

A man works in a skyscraper, with his office on the fifteenth floor. Every morning he takes a conventional lift, but instead of getting out on his floor, he stops at the tenth and walks up the remaining 5 floors. In the evening, when he takes the lift to go home, he travels directly from the fifteenth floor to the ground floor.
Why does he behave this way?

Recommended books

Marketing Management by Kotler and Keller

Blue Ocean Strategy

Lateral thinking